Photoionization detector automated zero level calibration

ABSTRACT

A method of detecting gas includes determining and storing, by a controller, a zero level of a photoionization detector using ambient air inflow when an ultraviolet lamp is in a turned OFF state, wherein the stored zero level is based on an ambient temperature; sampling, by the controller, an output of a detector electrode of the photoionization detector when the ultraviolet lamp is in a turned ON state; and comparing the sampled output of the detector electrode to the stored zero level to determine if a threshold concentration of a gas is present.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/090,391 filed on Oct. 1, 2018, which is a national phase entry ofInternational Application No. PCT/US2016/044614, filed Jul. 29, 2016,each of which is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Photoionization detectors (PIDs) employ a lamp to emit photons thationize gases in the proximity of detector electrodes. An electric fieldis established between the plates of the electrodes by an appliedvoltage bias. The electric field induces ionized particles to move toone or another plate, thereby establishing an electric current betweenthe electrodes. The electric current can be processed to extractindication of the presence of gas. For example, PIDs may be used todetect the presence and/or concentration of volatile organic compounds(VOCs) which can pose a threat to human beings.

SUMMARY

In an embodiment, a method of detecting gas with a photoionizationdetector (PID) system is disclosed. The method comprises powering on aphotoionization detector, turning off an ultraviolet lamp of thephotoionization detector by a controller of the photoionization detectorsystem and keeping it turned off during the zero calibration procedure,flowing ambient air from a surrounding environment by a fan of thephotoionization detector system past a detector electrode of thephotoionization detector, processing an output of the detector electrodeby the controller to determine a zero level of the photoionizationdetector, and storing the zero level by the controller in a memory ofthe photoionization detector system, wherein the photoionizationdetector in a detecting mode compares an output of the detectorelectrode to the zero level to determine if a threshold concentration ofa gas is present.

In another embodiment, a photoionization detector (PID) system isdisclosed. The photoionization detector comprises a detector electrodethat outputs a signal, an ultraviolet lamp, a lamp drivercommunicatively coupled to the ultraviolet lamp and configured to turnthe ultraviolet lamp on and off in response to a control input, acontroller that is communicatively coupled to the output signal of thedetector electrode and to the control input of the lamp driver, thatoutputs an indication of gas detection based on the output signal of thedetector electrode and based on a zero calibration level stored in thephotoionization detector system, and a zero calibration applicationstored in a memory of the photoionization detector system. When executedby the controller, the zero calibration application turns off anultraviolet lamp of the photoionization detector system during a zerocalibration procedure, processes the output signal of the detectorelectrode, while ambient air from the surrounding environment flows pastthe detector electrode, to determine a zero level of the photoionizationdetector system, and stores the zero level in the photoionizationdetector system.

In yet another embodiment, a method of detecting presence of a gas by aphotoionization detector (PID) system is disclosed. The method comprisespowering on a photoionization detector, turning off an ultraviolet lampof the photoionization detector by a controller of the photoionizationdetector system during the zero calibration procedure, flowing ambientair from a surrounding environment by a fan of the photoionizationdetector system past a detector electrode of the photoionizationdetector, processing an output of the detector electrode by thecontroller to determine a zero level of the photoionization detector,and storing the zero level by the controller in a memory of thephotoionization detector system, wherein the photoionization detectorsystem in a detecting mode compares an output of the detector electrodeto the zero level to determine if a threshold concentration of a gas ispresent. The method further comprises, after the zero level is stored,turning the ultraviolet lamp on and off periodically by the controller,after the zero level is stored, analyzing by the controller the samplingof the output of the detector electrode, determining by the controller aconcentration of gas based on the stored zero level and based on theanalyzing of the output of the detector electrode after the zero levelis stored, and outputting a gas detection indication by the controllerbased on the determination of the concentration of gas.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, referenceis now made to the following brief description, taken in connection withthe accompanying drawings and detailed description, wherein likereference numerals represent like parts.

FIG. 1 is a block diagram of a photoionization detector system accordingto an embodiment of the disclosure.

FIG. 2 is a flow chart of a method according to an embodiment of thedisclosure.

FIG. 3 is a flow chart of another method according to an embodiment ofthe disclosure.

FIG. 4 is a block diagram of a system according to an embodiment of thedisclosure.

FIG. 5 is an illustration of a portion of a photoionization detectoraccording to an embodiment of the disclosure.

FIG. 6 is an illustration of wave forms according to an embodiment ofthe disclosure.

FIG. 7 is a flow chart of a method according to an embodiment of thedisclosure.

DETAILED DESCRIPTION

It should be understood at the outset that although illustrativeimplementations of one or more embodiments are illustrated below, thedisclosed systems and methods may be implemented using any number oftechniques, whether currently known or not yet in existence. Thedisclosure should in no way be limited to the illustrativeimplementations, drawings, and techniques illustrated below, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

The present disclosure teaches a photoionization detector (PID) thatperforms zero level calibration without using specialized gas butinstead simply uses the ambient air, whatever gases it may contain atthe time. This is in contrast to known methods that entail providing aspecial source of calibration gas such as nitrogen. Providingcalibration gas can be expensive and complicates the process ofcalibrating the HD. The PID disclosed herein may be provided in the formfactor of a handheld device that may be carried by a worker in apotentially hazardous work environment where dangerous gases such asbenzene, toluene, gasoline, fuel oil, diesel fuel, or other volatileorganic compounds (VOCs) may present a hazard to a worker. Theseenvironments, without limitation, may include oil refineries, chemicalplants, manufacturing plants, and others. In some cases, the PID of thepresent disclosure may be mounted separately from human beings inportions of an infrastructure and may be communicatively coupled to amonitoring system.

The principle of operation of a PID is to radiate ultraviolet light ontoa flow of gas from an environment proximate to a pair of electricallybiased electrodes. If VOCs are present, the ultraviolet gas ionizes someof the VOC gas, the ions are collected at one or the other electrodeproducing an electric current that may be amplified and filtered andanalyzed to determine a magnitude of electric current which representsthe concentration of VOCs. The greater the current, the greater theconcentration of VOCs. A zero level may be determined during calibrationand stored in the processor or memory of the PID. When detectingconcentration of VOCs, the electric current level is compared to thezero level that was stored to determine the concentration of gas.

The prior art method of performing zero calibration entails providing agas which does not ionize in response to radiation with ultravioletlight and hence provides no incremental electric current in theelectrodes. The current disclosure teaches turning off the ultravioletlamp while performing the zero calibration. When this is done, there issubstantially no incremental electric current due to ionization in theelectrodes. Even if there may be VOCs present, since the ultravioletlamp is turned off, the VOCs are not ionized and there is little or noincremental electric current. This provides the condition desired todetermine an electric current level that is present when no ions arepresent. This process can be analogized to determining a tare weight formeasuring a weight in a container—the weight of the container issubtracted from the combined weight of the container and the contents ofthe container to determine the weight of the contents alone.

Turning now to FIG. 1, a photoionization detector (PID) system 1 isdescribed. In an embodiment, the MD system 1 comprises a controller 2, aphotoionization detector 4, a fan 6, a battery 8 or external powersupply, a visual display 10, and an input device 12. The photoionizationdetector system 1 may be similar in some aspects to the PID system 100described below with reference to FIG. 4, FIG. 5, FIG. 6, and FIG. 7.Here the emphasis is on the zero level calibration aspects of the MDsystem 1; below the emphasis is on the components of the PID system 100and their function after the zero level has been determined.

Gas from the ambient environment is drawn in past the photoionizationdetector 4 by the fan 6. During zero calibration, the ultraviolet lampin the photoionization detector 4 is turned off and hence any gas, forexample any VOCs, present in inflowing air is not ionized because thereis no ultraviolet light radiation to ionize the gas molecules. Theelectrical output of the photoionization detector 4 is measured orsampled by the controller 2 during this zero calibration process (i.e.,while the ultraviolet lamp is turned off), and the zero level is storedin the controller 2 and/or a memory communicatively coupled to thecontroller 2. In an embodiment, the zero level may be a count associatedwith the zero level. In an embodiment, the zero level may be a digitalvalue output by an analog-to-digital converter of the photoionizationdetector 4. The PID system 1 may be powered by the battery 8 or by anexternal power supply (i.e., in the case that the PID system 1 is not ahandheld device but is coupled to an infrastructure in a refinery ormanufacturing plant). The visual display 10 may provide visual feedbackthat the zero calibration process has been started and when the zerocalibration process has completed.

The zero level may be determined by maintaining the ultraviolet light inthe photoionization detector 4 may be held off through the entire timeduration of the zero level determination process. Alternatively, in anembodiment, the ultraviolet light may be turned off and on with apredefined on duty cycle, and the electrical output of thephotoionization detector 4 is captured while the ultraviolet light isturned off, for example after the ultraviolet light has been turned offlong enough for deionization to have substantially completed. Thecaptured output of the photoionization detector 4 is then used todetermine the zero level.

A worker may use the input device 12, for example a keypad or otherinput device, to initiate the zero calibration process at the start of awork day, at the start of a work week, or on some other schedule. Thevisual display 10 may also provide alerts to the presence of hazardousgas, for example the presence of VOCs. The visual display 10 may providean indication of the concentration of gas, for example quantified inparts per billion (ppb) or in parts per million (ppm). The visualdisplay 10 and/or an aural alert (not shown) may provide an attentiongetting alert when the concentration of gas exceeds a predefinedconcentration threshold. For example, a red indication may flash on thevisual display 10 and/or an alarm may sound. In an embodiment, the PIDsystem 1 may further comprise a vibrator (not shown) that may vibrate toconvey an alert to the worker in a high-noise work environment where anaural alert may be missed by a worker.

The zero calibration process may be performed over a time duration ofabout 1 minute, over a time duration of about 5 minutes, over a timeduration of about 15 minutes, over a time duration of about 1 hour, overa time duration of about 4 hours, over a time duration of about 12hours, over a time duration of about 24 hours, or over a time durationthat is intermediate between any two of these time durations.

The determination of the gas concentration by the controller 2 can beperformed in a manner such as the following:

Gas Concentration=Sensitivity×(Count_(gas)−Count_(zero))  EQ 1

Where Count_(zero) is the stored zero level, and where (Count_(gas) isthe value of the level or count of sensed gas sensed by thephotoionization detector during gas sensing. As discussed further below,(Count_(gas) may be the value of the level or count of sensed gasdetermined shortly after the ultraviolet lamp has been turned off. Asdiscussed further below, the ultraviolet lamp may be turned off and onperiodically rather than left on continuously to conserve and extendbattery power. For example, the on duty cycle of the ultraviolet lampmay be less than 10%. For example, the on duty cycle of the ultravioletlamp may be less than 2%. The reduced on duty cycle of the ultravioletlamp can also extend the life of the ultraviolet lamp and slow the rateof deposit of polymer deposition on the ultraviolet lamp and/or lampwindow. In an embodiment, the ultraviolet lamp may be a vacuumultraviolet (VUV) lamp.

By performing the zeroing procedure, the effect of ambient temperaturechanges can be readily adapted to by the PID system 1. For example, aworker may initiate a zeroing procedure for the PH) system 1 when movingfrom a first work area having a first ambient temperature to a secondwork area having a second ambient temperature. Alternatively, the HDsystem 1 may sense external temperature and adapt the zero level ofvalue Count_(zero) algorithmically based on sensed external temperatureaccordingly.

Turning now to FIG. 2 a method 50 for detecting a gas with thephotoionization detector system 1 is described. At block 52, aphotoionization detector is powered on. At block 54, an ultraviolet lampof the photoionization detector is turned off and kept turned off duringthe zero calibration procedure. Alternatively, the photoionizationdetector is turned off and on alternatively, with the on duty cyclebeing less than 50%, less than 10%, or less than 2% of the period of theon-off periodic cycle. At block 56, ambient air is flowed from asurrounding environment by a fan of the photoionization detector past adetector electrode of the photoionization detector. At block 58, anoutput of the detector electrode is processed to determine a zero levelof the photoionization detector. The output of the detector electrode issampled at a time when the ultraviolet light is turned off, for examplea predefined duration of time after the ultraviolet light is turned offto allow most ionized gas molecules to deionize. At block 60, the zerolevel is stored in a memory of the photoionization detector system 1,wherein the photoionization detector system 1 in a detecting modecompares an output of the detector electrode to the zero level todetermine if a threshold concentration of a gas is present. In anembodiment, the process of method 50 is performed each time thephotoionization detector system 1 is powered on. In an embodiment, theprocess of method 50 may further be initiated and performed in responseto a user input using the input device 12, for example on the occasionof the user moving from a first work environment to a second workenvironment (e.g., from an indoor work environment to an outdoor workenvironment.

Turning now to FIG. 3, a method 70 for detecting presence of a gas by aphotoionization detector system 1 is described. At block 72, aphotoionization detector is powered on. At block 74, an ultraviolet lampof the photoionization detector is turned off by a controller of thephotoionization detector system 1 and keeping it turned off during thezero calibration procedure. Alternatively, the photoionization detectoris turned off and on alternatively, with the on duty cycle being lessthan 50%, less than 10%, or less than 2% of the period of the on-offperiodic cycle. At block 76, ambient air from a surrounding environmentis flowed by a fan of the photoionization detector system 1 past adetector electrode of the photoionization detector. At block 78, anoutput of the detector electrode is processed by the controller todetermine a zero level of the photoionization detector. The output ofthe detector electrode is sampled at a time when the ultraviolet lightis turned off, for example a predefined duration of time after theultraviolet light is turned off to allow most ionized gas molecules todeionize.

At block 80, the zero level is stored by the controller in a memory ofthe photoionization detector system 1, wherein the photoionizationdetector system 1 in a detecting mode compares an output of the detectorelectrode to the zero level to determine if a threshold concentration ofa gas is present. At block 82, after the zero level is stored, theultraviolet lamp is turned on and off periodically by the controller. Inan embodiment, the photoionization detector is turned off and onalternatively, with the on duty cycle being less than 50%, less than10%, or less than 2% of the period of the on-off periodic cycle. Atblock 84, after the zero level is stored, the controller analyzes anoutput of the detector electrode. At block 86, the controller determinesa concentration of gas based on the stored zero level and based on theanalyzing of the output of the detector electrode after the zero levelis stored. At block 88, the controller outputs a gas detectionindication based on the determination of the concentration of gas. Forexample, the visual display 10 may indicate a concentration of gas inparts per billion (ppb) or in parts per million (ppm). Alternatively,the photoionization detector system 1 may present an alarm such as byvisual alert on the visual display 10, an aural alert, and/or avibration alert, if the concentration of gas exceeds a predefinedalerting threshold.

In an embodiment, a lamp driver is turned on and off by a controller,turning on and off the MD lamp. The PID lamp is turned on for arelatively short duty time, for example less than 10% of the time. Thisreduces the power load on the battery. Additionally, this extends thelife of the PID lamp and reduces the rate of polymer deposition on thePID lamp and/or PID lamp window. A signal conditioning circuit thatreceives the output of a HD sensor and/or PID electrodes is turned offand on by the controller, enabling signal sampling, conditioning, andoutputting of signal to the controller for determining an indication ofpresence or absence of gas. The controller turns the signal conditioningcircuit on only after the PID lamp driver (and hence the PID lamp) isturned off. Because the PID lamp driver and/or PID lamp, when turned on,create electric noise in the PID, sampling and signal conditioning whenthe HD lamp driver and PID lamp are turned off reduces the noise thatenters the signal conditioning circuit. Because there is less electricnoise, the filtering time constant of the signal conditioning circuitcan be substantially reduced, thereby increasing the response time ofthe PID.

Turning now to FIG. 4, a PID system 100 is described. In an embodiment,this MD system 100 may be substantially similar to the HD system 1described above with reference to FIG. 1, FIG. 2, and FIG. 3. In anembodiment, the PID system 100 comprises a controller 102, a lamp driver104, an ultraviolet (UV) lamp 106, an electrode 108, a filter 112, andan analog-to-digital converter 116. The controller 102 may be amicrocontroller, an application specific integrated circuit (ASIC), aprogrammable logic device (PLD), a field programmable gate array (FPGA),or some other logic processor. The lamp driver 104 is configured toprovide power and/or stimulate the UV lamp 106 to emit UV light. In anembodiment, the UV lamp 106 may be associated with a window (not shown)through which UV light emitted by the UV lamp 106 passes beforeradiating the vicinity of the electrode 108. The electrode 108 maycomprise at least two parallel plates of electrodes that are provided astable direct current (DC) bias voltage.

When the UV lamp 106 is turned on, UV light emitted by the UV lamp 106ionizes gases, if present, in the vicinity of the electrode 108, and anelectric field between the plates of the electrode 108 induces a currentflow that is proportional to the presence of ionized gas molecules. Notethat when the UV lamp 106 is turned off, the process of ionization stopsbut the already ionized gas molecules do not immediately deionize, hencea current flow may continue between the plates of the electrode 108 forsome time after the UV lamp 106 is turned off, if there are gasespresent (e.g., if volatile organic compounds (VOCs) are present). Whenthe UV lamp 106 is turned on, electric noise is induced into the PID bythe UV lamp 106 and/or the lamp driver 104. When the UV lamp 106 andlamp driver 104 are turned off by the controller 102, this source ofelectric noise is eliminated.

The controller 102 turns the lamp driver 104 on and off via a firstcontrol signal 103. In an embodiment, the controller 102 turns the lampdriver 104 on and off periodically and with an on duty cycle of lessthan 10%. As is understood by one skilled in the art, a duty cycle is arepresentation of the amount of time something is turned on versusturned off, often represented as a percentage. As an example, if theperiod is 1 second (S), a 10% on duty cycle would turn the lamp driver104 on for about 100 milliseconds (mS) and off for about 900 mS in every1 S period. In another example, if the period is 1 second, a 1% on dutycycle would turn the lamp driver 104 on for about 10 mS and off forabout 990 mS in every 1 S period. As another example, if the period is100 mS, a 10% on duty cycle would turn the lamp driver 104 on for about10 mS and off for about 90 mS in every 100 mS period. In anotherexample, if the period is 100 mS, a 1% on duty cycle would turn the lampdriver 104 on for about 1 mS and off for about 99 mS in every 100 mSperiod.

The filter 112 and analog-to-digital converter 116 may be considered tobe a signal conditioning circuit. In an embodiment, some or all of thefunctions of signal conditioning may be performed in the controller 102.For example, the controller 102 may perform digital filtering of inputsfrom the analog-to-digital converter 116. The filter 112 and theanalog-to-digital converter 116 may be turned on and off by thecontroller 102. The filter 112 and/or the analog-to-digital converter1.16 may be turned on and off with less than a 1°/0 on duty cycle by thecontroller 102, for example by a second control signal 111. In anembodiment, the controller 102 turns the filter 112 and/or theanalog-to-digital converter 116 on after the lamp driver 104 and the UVlamp 106 have been turned off. In an embodiment, the filter 112 is leftturned on continuously and the analog-to-digital converter 116 is turnedon after the lamp driver 104 and the UV lamp 106 have been turned off.

In an embodiment, the analog-to-digital converter 116 is turned on bythe controller 102 a predefined time delay after the lamp driver 104 andthe UV lamp 106 have been turned off. In an embodiment, the predefinedtime delay is related to a time constant of the filter 112, for examplethe predefined time delay is one time constant of the filter 112, twotime constants of the filter 112, or some other time duration. As isknown to one skilled in the art, the time constant of a filter is thetime for a filter to reach a threshold portion of its final output valuein response to an input value. In an embodiment the time constant of thefilter 112 may be less than 50 mS. In an embodiment, the time constantof the filter 112 may be less than 5 mS. In an embodiment, the timeconstant of the filter 112 may be less than 1 mS. By turning theanalog-to-digital converter 116 on after the lamp driver 104 and the UVlamp 106 are turned off, the noise created by the lamp driver 104 andthe UV lamp 106 may be kept out of the signal conditioning circuit andthe time constant of the filter 112 can be reduced, thereby producing amore rapid response in the signal conditioning circuit. The electrode108 outputs a detector electrode signal 110 that is input to the filter112. The filter 112 outputs a filtered detector electrode signal 114that is input to the analog-to-digital converter 116. Theanalog-to-digital converter 116 outputs a digital signal 118 to thecontroller 102.

Prior art PIDs may leave the UV lamp on continuously. By turning the UVlamp 106 on for a reduced fraction of time—for example for 1/10 theamount of time—the electric power load on a battery 132 that providespower to the PID system 100 may be reduced and a battery life cycle (orrecharge cycle) be extended. Additionally, by turning the UV lamp 106 onfor a reduced fraction of time, the life of the UV lamp 106 may beextended before it burns out. Further, while the UV lamp 106 is turnedon in the presence of VOCs, some polymers may be formed duringionization, and these polymers may deposit and accumulate on the UV lamp106 and/or on a window of the UV lamp. The deposition of polymers on theUV lamp 106 and/or a window of the UV lamp may degrade the performanceof the UV lamp 106.

When the presence of gas is detected by the controller 102 it may outputa gas detection alert or signal 120. This signal 120 may cause anindication to be presented by an output device 122 of the PID system100, for example to a human being associated with the PID system 100.For example, the PID system 100 may be a personal portablephotoionization detector carried by a worker in an environment that mayexpose the worker to VOC hazards. The output device 122 may comprise anaural alert device 124 and/or a visual alert device 126. In anembodiment, the PID system 100 further comprises a microprocessor 128that receives the signal 120 and provides control signals to the outputdevice 122. The microprocessor 128 may also write records to a memory130, for example periodic log entries recording levels of gas detectionindexed by time. Such log entries may be useful and/or required forauditing safety of work environments, for example.

Turning now to FIG. 5, further details of the PID system 100 aredescribed. In an embodiment, the filter 112 may comprise an amplifier160 that boosts the amplitude of the detector electrode signal 110. Inan embodiment, the filter 112 further comprises a first resistor 162, asecond resistor 164, and a capacity 166. It is understood that thefilter 112 may be implemented in other ways than that illustrated inFIG. 5.

Turning now to FIG. 6, a wave form diagram 180 is described. A firstwave form 182 represents the first control signal 103 output by thecontroller 102 for enabling or turning on the lamp driver 104 and henceturning on the UV lamp 106. The first wave form 182 is high at label 186and enables or turns on the lamp driver 104. A second wave form 184represents the second control signal 111 output by the controller 102 toenable or turn on the filter 112 and/or the analog-to-digital converter116. The second wave form 184 is high at label 192 and enables or turnson the filter 112. In an embodiment, the filter 112 is left turned onand the second control signal 111 turns on and off the analog-to-digitalconverter 116 alone. It is understood that the wave form diagram 180does not represent the whole duration of a period of the wave forms 182,184. For example, if the first control signal 103 has a 1% on dutycycle, the portion of the complete wave form period shown in FIG. 6 mayonly comprise about 1/33th of a period. The wave form diagram 180illustrates the relationship between the time duration of the oninterval of the first control signal 103 and the time duration of the oninterval of the second control signal 111. The wave form diagram 180further illustrates the timing sequence of the on interval of the firstcontrol signal 103 and the on interval of the second control signal 111.

The on interval of the first control signal 1.03—and hence the oninterval of the UV lamp 106—is significantly longer than the on intervalof the second control signal 111—and hence the on interval of at leastthe analog-to-digital converter 116. In an embodiment, the on intervalof the first control signal 103 may be at least five times longer thanthe on interval of the second control signal 111. In an embodiment, theon interval of the first control signal 103 may be at least fifty timeslonger than the on interval of the second control signal 111. In anembodiment, the on interval of the first control signal 103 may be atleast five hundred times longer than the on interval of the secondcontrol signal 111. In an embodiment, the first control signal 103 maybe on for about 10 mS (milliseconds) while the second control signal 111may be on for about 10 μS (microseconds).

The second control signal 111 is turned on after the first controlsignal 103 is turned off. In an embodiment, there is a time intervalbetween the first control signal 103 being turned off and the secondcontrol signal 111 being turned on. For example, the first controlsignal 103 may be turned off at time 188 and the second control signal111 may be turned on at time 190. The difference between the time 188and time 190 may be a predefined time interval related to the constantof the filter 112, for example about one time constant of the filter112, about two time constants of the filter 112, about three timeconstants of the filter 112, or some other number. Delaying turning onthe second control signal 111 some predefined period of time afterturning off the first control signal 103 may result in excluding noiseassociated with the UV lamp 106 being turned on from the sampling and/orcapture of the output of the detector electrode signal 110 and mayresult in the filter 112 reaching a steady state or a settled value ofthe output of the detector electrode signal 110. It is noted that it isundesirable to extend the predefined period of time (between time 188and time 190) excessively, because over time the ionized gases deionize.Thus, the predefined period of time should be long enough to allow thefilter 112 to settle after the turning off of the first control signal103 and hence turning off of the UV lamp 106 and elimination of theelectric noise it produces while at the same time short enough to avoidexcessive deionization of gases ionized while the UV lamp 106 was turnedon. In combination with the present disclosure, one skilled in the artwill readily determine a suitable time interval for the offset betweentime 188 and time 190. As an example, a time interval of about threetimes the time constant of the filter 112 may be suitable in someembodiments. An another example, a time interval of about 1.5 times thetime constant of the filter 112 may be suitable in other embodiments.

Turning now to FIG. 7, a method 200 is described. The method 200 maydescribe a method of using the P1D system 100. In an embodiment, a humanbeing may carry the PID system 100 with him or her into a workenvironment to warn of the presence of hazardous gases, for example warnof the presence of VOCs. Without limitation, VOCs may comprise varioussolvents, fuels, degreasers, plastics, heat transfer fluids, lubricants,and others. VOCs may be harmful to human beings if inhaled and/orinhaled in concentrations exceeding a predefined exposure threshold.VOCs may present a risk of explosion or fire, for example when presentin concentrations exceeding a predefined threshold. The PlD system 100may be used to monitor industrial hygiene and safety, environmentalcontamination and remediation, hazardous materials handling, ammoniadetection, and refinery environments. A plurality of PID systems 100 maybe used in combination, each tuned to a different kind of gas or VOCbased on the primary wavelength of its UV lamp 106.

At block 202, an ultraviolet lamp is turned on and off periodically by acontroller, where the on duty cycle is less than 100%. For example, theUV lamp 106 is turned on and off periodically by the controller 102.Said in other words, the UV lamp 106 is turned on and off periodicallyby the lamp driver 104, and the lamp driver 104 is turned on and offperiodically by the controller 1.02. At block 204, while the ultravioletlamp is turned off, an output of a detector electrode is sampled. Theoutput of the detector (e.g., the detector electrode signal 110) may besampled after a predefined period of time after the UV lamp 106 isturned off, as described further above with reference to FIG. 3. Thesampling of the output of the detector may be performed over arelatively short period of time, for example for about 10 μS or about100 μS. The sampling may be performed with an on duty cycle of less than1%. In an embodiment, the sampling may be performed with an on dutycycle of less than 0.01%.

At block 206, the controller analyzes the sampling of the output of thedetector electrode. For example, the controller 102 analyzes thedetector electrode signal 110 at least indirectly via the signalconditioning circuit (i.e., filter 112 and analog-to-digital converter116). At block 208, the controller outputs a gas detection indicationbased on the analysis of the sampling of the output of the detectorelectrode. It is understood that the method 200 comprises repeating theprocessing of blocks 204, 206, 208 on an ongoing basis.

At block 210, optionally (e.g., under the appropriate circumstances,where concentration of gas above a predefined threshold is detected),presenting an alert of presence of detected gas based on the gasdetection indication output by the controller. The alert may bepresented by the output device 122, for example by the aural alertdevice 124 and/or the visual alert device 126. In an embodiment, themethod 200 may further comprise periodically recording levels ofdetected gas to the memory 130, for example storing logs to the memory1.30.

In an embodiment, the PID system 100 may be manufactured by mechanicallysecuring the controller 102, lamp driver 104, UV lamp 106, detectorelectrode 108, filter 112, analog-to-digital converter 116, outputdevice 122, microprocessor 128, and/or memory 130 to a circuit boardand/or package. Suitable electrical lines and connections may beprovided between components. The UV lamp 106 may be disposed on thecircuit board and/or within the package so as to be proximate to thedetector electrode 108 and to radiate UV light towards the detectorelectrode 108. A fan and air channel may be disposed within the packageto direct environmental gases towards the detector electrode 108 and UVlamp 106 when the PID system 100 is in use. The battery 132 may beassembled into the system 100 at a time different from manufacture, forexample at time of first use by a human being.

In an embodiment, a photoionization detector is disclosed. Thephotoionization detector may comprise a detector electrode that outputsa signal, an ultraviolet lamp, a lamp driver communicatively coupled tothe ultraviolet lamp and configured to turn the ultraviolet lamp on andoff in response to a control input, and a controller that iscommunicatively coupled to the output signal of the detector electrodeand to the control input of the lamp driver, that outputs an indicationof gas detection based on the output signal of the detector electrode,and that turns the lamp driver on and off with an on duty cycle of lessthan 10%. In an embodiment, the controller turns the lamp driver on andoff with an on duty cycle of less than 2%. In an embodiment, thephotoionization detector further comprises a filter having a timeconstant of less than 5 milliseconds (mS), where the filter receives thesignal output by the detector electrode and outputs a filtered detectorelectrode signal, wherein the controller is communicatively coupled tothe output signal of the detector electrode via the filter and outputsthe indication of gas detection based on the filtered detector electrodesignal output by the filter. In an embodiment, the photoionizationdetector further comprises an analog-to-digital converter that outputs adigital filtered detector electrode signal, wherein the controller iscommunicatively coupled to the filtered detector electrode signal viathe analog-to-digital converter and outputs the indication of gasdetection based on the digital filtered detector electrode signal outputby the analog-to-digital converter, and wherein the controller turns theanalog-to-digital converter on and off to achieve an on duty cycle ofless than 1% and wherein the controller turns the analog-to-digitalconverter on when the lamp driver is turned off and turns theanalog-to-digital converter off before the lamp driver is next turnedon. In an embodiment, the controller turns the analog-to-digitalconverter on for less than 15 microseconds (μS). In an embodiment, thefilter comprises an electronic amplifier.

In an embodiment, a method of detecting presence of gas with aphotoionization detector (PID), comprises turning an ultraviolet lamp onand off periodically by a controller, where the on duty cycle is lessthan 10°/o; while the ultraviolet lamp is turned off, sampling an outputof a detector electrode; analyzing by the controller the sampling of theoutput of the detector electrode; and outputting a gas detectionindication by the controller based on the analysis of the sampling ofthe output of the detector electrode. In an embodiment, the methodfurther comprises filtering the output of the detector electrode by afilter having a time constant of less than 50 milliseconds (mS), whereinthe filtered output of the detector electrode is sampled and provided tothe controller for analyzing. In an embodiment, the sampling is enabledby the controller with a duty cycle that is less than 1%. In anembodiment, the sampling comprises analog-to-digital conversion. In anembodiment, the on duty cycle of the ultraviolet lamp is less than 2%.

In an embodiment, a photoionization detector comprises a detectorelectrode that outputs a signal, an ultraviolet lamp, a lamp drivercommunicatively coupled to the ultraviolet lamp and configured to turnthe ultraviolet lamp on and off in response to a control input, a filterthat receives the signal output by the detector electrode and outputs afiltered detector electrode signal, where the filter has a time constantof less than 50 milliseconds (mS), and a controller that iscommunicatively coupled to the filtered detector signal output by thefilter and to the control input of the lamp driver, that outputs anindication of gas detection based on the filtered detector electrodesignal output by the filter, and that turns the lamp driver on and off.In an embodiment, the filter has a time constant of less than 5 mS. Inan embodiment, the controller turns the lamp driver on and off toachieve an on duty cycle of less than 10%. In an embodiment, thephotoionization detector further comprises an analog-to-digitalconverter that is coupled to the filter and to the controller, thatconverts the filtered detector electrode signal from the filter to adigital filtered detector electrode signal, and that outputs the digitalfiltered detector electrode signal to the controller, wherein thecontroller outputs the indication of gas detection based on the digitalfiltered detector electrode signal output by the analog-to-digitalconverter and wherein the controller turns the analog-to-digitalconverter on and off to achieve an on duty cycle of less than 1% andwherein the controller turns the analog-to-digital converter on when thelamp driver is turned off and turns the analog-to-digital converter offbefore the lamp driver is next turned on.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods may beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another system,or certain features may be omitted or not implemented.

Also, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as directly coupled or communicating witheach other may be indirectly coupled or communicating through someinterface, device, or intermediate component, whether electrically,mechanically, or otherwise. Other examples of changes, substitutions,and alterations are ascertainable by one skilled in the art and could bemade without departing from the spirit and scope disclosed herein.

1. A method of detecting gas, comprising: determining and storing, by acontroller, a zero level of a photoionization detector using ambient airinflow when an ultraviolet lamp is in a turned OFF state, wherein thestored zero level is based on an ambient temperature; sampling, by thecontroller, an output of a detector electrode of the photoionizationdetector when the ultraviolet lamp is in a turned ON state; andcomparing the sampled output of the detector electrode to the storedzero level to determine if a threshold concentration of a gas ispresent.
 2. The method of claim 1, further comprising, adapting the zerolevel algorithmically based on a change in the ambient temperature. 3.The method of claim 1, further comprising, after storing the zero level,turning on and off the ultraviolet lamp by the controller with an onduty cycle of less than 50 percent; and presenting an alert by thephotoionization detector system.
 4. The method of claim 2, wherein thecontroller determines that a threshold concentration of volatile organiccompounds (VOCs) is present.
 5. The method of claim 1, furthercomprising, after storing the zero level, turning on and off theultraviolet lamp by the controller with an on duty cycle of less than 10percent.
 6. The method of claim 1, further comprising, after storing thezero level, turning on and off the ultraviolet lamp by the controllerwith an on duty cycle of less than 2 percent.
 7. The method of claim 1,further comprising, displaying at least one of a visual and and an auralalert when the concentration of gas exceeds the threshold concentrationof the gas.
 8. A photoionization detector system, comprising: a lampdriver communicatively coupled to an ultraviolet lamp and configured toturn the ultraviolet lamp on and off in response to a control input; acontroller that is communicatively coupled to an output signal of adetector electrode and to the control input of the lamp driver; and azero calibration application, executed by the controller, configured to:turn off the ultraviolet lamp of the photoionization detector systemduring a zero calibration procedure wherein the zero calibrationapplication is stored in a memory of the photoionization detectorsystem, process a first output signal of the detector electrode todetermine a zero level of the photoionization detector system, store thezero level in the photoionization detector system, wherein the storedzero level is based on an ambient temperature, sample a second outputsignal of the detector electrode; and compare the sampled second outputsignal with the stored zero level to determine if a thresholdconcentration of a gas is present.
 9. The photoionization detectorsystem of claim 8, wherein the ultraviolet lamp comprises a vacuumultraviolet lamp.
 10. The photoionization detector system of claim 8,wherein the zero calibration application turns the ultraviolet lampalternately on and off during the zero calibration procedure.
 11. Thephotoionization detector system of claim 10, wherein the zerocalibration application turns the ultraviolet lamp on and off with an onduty cycle of less than 50%.
 12. The photoionization detector system ofclaim 10, wherein the zero calibration application turns the ultravioletlamp on and off with an on duty cycle of less than 10%.
 13. Thephotoionization detector system of claim 10, wherein the zerocalibration application turns the ultraviolet lamp on and off with an onduty cycle of less than 2%.